Device and method for expanding the spinal canal with spinal column stabilization and spinal deformity correction

ABSTRACT

Spinal canal expansion through pedicle lengthening in combination with spinal column stabilization, to treat spinal stenosis, spondylolisthesis, kyphosis, scoliosis or a major spinal rotational deformity, with or without a spinal fusion. A device or implant that includes a pedicle lengthening implant to decompress (expand) the spinal canal, and a bridge to connect two or more pedicle lengthening implants and/or pedicle screws or bone anchors to achieve simultaneous spinal stabilization across one or more vertebral segments. The bridge across the vertebral segments can include a longitudinal member, such as a plate or rod. The pedicle lengthening implant is originally made, or can be modified to, connect to the longitudinal member. Spinal deformity can be manipulated, through operation of one or more pedicle lengthening implants in respective vertebral segments, to improve a relative relationship between the respective vertebra segments, the longitudinal member then fixating the vertebral segments into a multi-level spinal construct.

RELATED APPLICATIONS

This application is a continuation-in-part (CIP) of U.S. Ser. No.12/624,946, filed Nov. 24, 2009; which application is acontinuation-in-part (CIP) of U.S. Ser. No. 11/656,790, filed Jan. 22,2007; which application is a continuation of U.S. Ser. No. 10/102,525,filed Mar. 19, 2002 (now U.S. Pat. No. 7,166,107).

This application also claims benefit of U.S. Provisional ApplicationSer. No. 61/318,441, filed Mar. 29, 2010. U.S. Ser. No. 12/624,946,filed Nov. 24, 2009, claims benefit of U.S. Provisional Application Ser.No. 61/117,726, filed Nov. 25, 2008. All of the above-identified relatedapplications are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to spinal surgery, and moreparticularly to a method and device for expanding the spinal canal whentreating spinal stenosis and for simultaneously providing fixationbetween vertebrae for fusion and non-fusion applications; namely, forcorrection of certain spinal deformities, such as kyphosis, scoliosis ora rotation deformity of the spinal column.

BACKGROUND OF THE INVENTION

Spinal stenosis is a common disease involving narrowing of the spinalcanal. This disease leads to compression of the spinal nerves andproduces symptoms of leg or back pain, walking problems, weakness and/ornumbness in the affected portions of the body. Many patients with spinalstenosis also have co-existent spinal problems such as a spinaldeformity or spinal instability.

Recently, pedicle lengthening methods and implants have been describedfor the treatment of spinal stenosis in U.S. Pat. No. 7,166,107, issuedJan. 23, 2007, entitled “Percutaneous Technique and Implant forExpanding the Spinal Canal;” and U.S. application Ser. No. 12/624,946,filed Nov. 24, 2009, (US Publication No. 2010/0168751), entitled“Method, Implant & Instruments for Percutaneous Expansion of the SpinalCanal.” In this US patent and US patent application, pedicle lengtheningmethods and implants (or devices) for expanding a stenotic spinal canalhave been disclosed. U.S. Pat. No. 7,166,107, and U.S. application Ser.No. 12/624,946 (US Publication No. 2010/0168751), are incorporatedherein by reference.

Although spinal canal expansion through pedicle lengthening allows anovel method for treating spinal stenosis, some patients with severespinal deformities due to spondylolisthesis, kyphosis, scoliosis or amajor rotational deformity of the spinal column may requirestabilization of the spinal column, with or without a spinal fusion. Forthe patient with a combination of spinal stenosis and instability, itwould be desirable to decompress (expand) the spinal canal using pediclelengthening and to achieve simultaneous fixation of the spine to performthe necessary stabilization. To stabilize the spine, the surgeonrequires an implant that bridges across one or more vertebral segmentsusing a longitudinal member, such as a plate or rod. By a novelmodification of the pedicle lengthening implant, connection to alongitudinal member can be achieved allowing simultaneous expansion ofthe spinal canal with stabilization of the spinal segment.

Another problem that the current invention addresses is the patient whohas undergone pedicle lengthening for the treatment of spinal stenosisin the past and develops instability or a significant spinal deformitythat requires stabilization of the lengthened spinal segments. In thissituation, it is desirable to use the already present spinal anchors(pedicle lengthening devices) as a point of fixation for the requiredspinal reconstructive procedure. By providing a novel means of attachinga longitudinal member (rod or plate) to the existing pedicle lengtheningdevices, this problem can be easily treated without the need to removethe pedicle lengthening devices.

Another problem that the current invention addresses is the need for animproved correction means when treating certain spinal deformities suchas kyphosis, scoliosis or a rotational deformity. Current techniques forcorrecting these deformities are either marginally effective or highlyinvasive. The current invention provides a novel means to correct thesedeformities and to simultaneously allow a spinal stabilization procedureto be performed, thus reconstructing the spine in an optimized fashion.

Another problem that the current invention addresses is the need for abiomechanically stronger fixation technique to be used in situations ofpoor bone quality (osteopenia or osteoporosis) or when major forces needto be applied to the spine. Current techniques for fixation of poorquality bone have major drawbacks and in many cases are marginallyeffective. The current invention provides a very strong bone anchor thatallows secure fixation that can be incorporated into a spinalstabilization construct.

The current disclosure describes a novel medical device and techniquefor lengthening of the pedicles to correct spinal stenosis whilesimultaneously allowing connection to a longitudinal member such as arod or plate for spinal stabilization through either fusion ornon-fusion techniques. In addition, this disclosure describes a methodand device to convert an existing pedicle lengthening device forattachment of a longitudinal member such as a rod or plate. Also, thisdisclosure describes the use of the pedicle lengthening device with anattached longitudinal member such as a plate or rod as a means tocorrect a kyphotic or rotational deformity of the spinal column.Finally, this disclosure describes the use of the pedicle lengtheningdevice as a biomechanically superior bone anchor for use in a spinalfixation construct.

SUMMARY OF THE INVENTION

The present invention comprises a novel medical device capable oflengthening the spinal pedicle and securing the pedicle to alongitudinal member such as a rod or plate to achieve fixation of two ormore vertebrae. The current invention is capable of correcting anarrowed spinal canal, while allowing the vertebral segment to beincorporated into a spinal stabilization construct. In addition, thedevice is useful when treating deformed spines (particularly thosespines with excessive kyphosis, scoliosis or a rotational deformity) andprovides a biomechanically superior vertebral anchorage compared to theuse of a traditional pedicle screw.

Embodiments of the present invention will be shown variously to:

allow expansion of the spinal canal (for the correction of spinalstenosis) and to allow fixation of the involved vertebra into a spinalstabilization construct;

provide an improved ability to correct a spinal deformity (particularlyscoliosis, kyphosis or a rotational deformity) while allowinglongitudinal fixation of the spinal column;

allow a surgeon to connect a longitudinal member (such as a plate orrod) onto a pedicle lengthening device so that a stabilization procedurecan be performed at the site of a prior pedicle lengthening without theneed to remove or revise the pedicle lengthening device;

allow a minimally invasive method to achieve both correction andstabilization of the spinal column; and

provide a biomechanically superior spinal anchor for use during spinalreconstructive procedures.

In one aspect of the present invention, a novel attachment mechanism isdescribed for the pedicle lengthening device to allow the device toincorporate a longitudinal member (such as a rod or plate) and thus beincorporated into a spinal stabilization construct.

In another aspect, a rod attachment mechanism is described which wouldallow a previously placed device to be incorporated into a spinalfixation construct.

In yet another aspect, a pedicle lengthening device is shown to correcta rotational or kyphotic deformity of the spinal column.

The present invention has many advantages over currently known methodsfor treating spinal instability, as would be seen withspondylolisthesis, kyphosis, scoliosis or a rotational deformity,including:

-   -   (1) both the correction of spinal stenosis and stabilization of        the spinal column can be performed through a single device        allowing a much broader range of spinal pathology to be        addressed;    -   (2) an existing pedicle lengthening device can be used as a        spinal anchor for a spinal stabilization procedure;    -   (3) spinal deformities such as kyphosis, scoliosis and        rotational deformities can be corrected using the pedicle        lengthening technique while allowing the pedicle lengthening        device to act as a spinal anchor and be incorporated into a        spinal fixation construct;    -   (4) a biomechanically stronger spinal anchor is provided that        can be used to attach a longitudinal member (such as a rod or        plate) to the spine; and    -   (5) a minimally invasive spinal device is provided that can        produce both decompression of stenotic regions of the spinal        canal in addition to spinal fixation for a spinal stabilization        procedure; both procedure being achieve through small or        percutaneous incisions.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings included herein are included for the purpose ofillustrating preferred embodiments of the current invention; however, itshould be clear that the invention is not limited to the precisearrangements or specific parts. Nor is the specific sequence of stepsshown required to practice the disclosed invention. All drawings arehereby included for illustration purposes only and in no way shouldlimit the scope of the invention.

FIG. 1 illustrates a perspective view of a pedicle lengthening andstabilization construct, in accordance with one embodiment of thepresent invention, implanted within two adjacent vertebrae that haveundergone pedicle lengthening;

FIG. 2 illustrates a perspective top view of the FIG. 1 embodiment,shown stabilizing two adjacent vertebrae through a rod linkage;

FIG. 3 illustrates a perspective side view of the FIG. 1 embodiment,again showing stabilization of two adjacent vertebrae that haveundergone pedicle lengthening;

FIG. 4 a illustrates an axial perspective view of a vertebra with arotation deformity;

FIG. 4 b illustrates an axial perspective view of the vertebra of FIG. 4a following correction of the rotation deformity by pedicle lengthening,in accordance with one embodiment of the invention, and stabilization ofthe vertebra to an adjacent vertebra;

FIG. 5 a illustrates a three segment portion of a spine with a kyphoticdeformity;

FIG. 5 b illustrates the three segment portion of the spine of FIG. 5 a,demarcating locations of corrective pedicle osteotomies; and

FIG. 5 c illustrates the three segment portion of the spine of FIG. 5 afollowing correction of the kyphotic deformity by pedicle lengthening,in accordance with one embodiment of the invention, and stabilization ofthe three segment portion by securing the pedicle lengthening implantswith a longitudinal member (rod).

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Referring now to the figures, where like numerals indicate likeelements, there is shown in FIG. 1 a perspective view of a pediclelengthening and stabilization construct, in accordance with oneembodiment of the present invention, implanted within two adjacentvertebrae that have undergone pedicle lengthening. Pedicle lengtheningimplants 2 can be seen implanted into the pedicles 9 of the two adjacentvertebrae.

The pedicle lengthening implants 2 have been extended to create a gap 3at the base of the pedicle 9 and thus expand the dimensions of thespinal canal 15. Techniques and implants (devices) for pediclelengthening have been described in detail in U.S. Pat. No. 7,166,107,issued Jan. 23, 2007, entitled “Percutaneous Technique and Implant forExpanding the Spinal Canal;” and in U.S. application Ser. No.12/624,946, filed Nov. 24, 2009, (US Publication No. 2010/0168751),entitled “Method, Implant & Instruments for Percutaneous Expansion ofthe Spinal Canal.” U.S. Pat. No. 7,166,107, and U.S. application Ser.No. 12/624,946 (US Publication No. 2010/0168751), are incorporatedherein by reference.

The pedicle lengthening implants 2 are seen attached to screw headconnectors 21, capable of accommodating and securing rods 17 that linkthe pedicle lengthening implants 2 together, thus securing andstabilizing the attached vertebrae. Also shown in FIG. 1 is lockingmechanism 23, that secures each pedicle lengthening implant 2 in itsextended position.

FIG. 2 illustrates a perspective top view of the FIG. 1 embodiment,shown stabilizing two adjacent vertebrae through a rod linkage. In FIG.2, an upper portion of the pedicle lengthening implants 2 can be seen.Also shown is secure attachment of each screw head connector 21 to arespective rod 17, thereby linking and securing adjacent vertebrae viaattachment of the adjacent pedicle lengthening implants 2. The rods 17are secured into respective screw head connector 21 by a locking nut 25.

FIG. 3 illustrates a perspective side view of the FIG. 1 embodiment,again showing stabilization of two adjacent vertebrae that haveundergone pedicle lengthening. Pedicle lengthening implants 2 are shownimplanted within the pedicles 9 of two adjacent vertebrae. The pediclelengthening implants 2 have been expanded to lengthen the pedicles 9 andthus expand the spinal canal 15 (shown in FIG. 1) and the neural foramen27. The pedicle lengthening implants 2 each have attached thereto ascrew head connector 21, secured to a rod 17 that spans a joint betweenthe two vertebrae, thus stabilizing the spinal segment.

FIG. 4 a illustrates an axial perspective view of a vertebra with arotation deformity. It will be evident to one skilled in the art ofspinal surgery that there is an asymmetry to the vertebra illustrated inFIG. 4 a, where a smaller pedicle gap 3 is shown on the right side ofthe vertebra (as shown in FIG. 4 a) and a larger pedicle gap 3 is shownon the left side. The spinous process 5, lamina 11, and the vertebralbody 1 of the vertebra also exhibit a rotationally deformed morphology.It should be clear that this type of deformity is common to patientswith spinal curvature (scoliosis). In FIG. 4 a, pedicle lengtheningimplants 2, each including jack screws 19 and ventral implants 29, areshown implanted into the pedicles 9 of each vertebra. The jack screw 19portion of the pedicle lengthening implant 2 is shown extending from thedorsal surface of the pedicle lengthening implants 2.

FIG. 4 b illustrates an axial perspective view of the vertebra of FIG. 4a following correction of the rotation deformity by pedicle lengthening,in accordance with one embodiment of the invention, and afterstabilization of the vertebra to an adjacent vertebra. In FIG. 4 b, itwill be evident to one skilled in the art that the rotation deformityshown in FIG. 4 a has been corrected and that symmetry has beenrestored. By differential turning of the jack screws 19, the pediclegaps 3 have been equalized and a normal relationship between the spinousprocess 5 and the vertebral body 1 has been created. The rotationaldeformity correction gained through the use of the pedicle lengtheningimplants 2 has been stabilized by the attachment of screw headconnectors 21 and rods 17, which have been secured to maintain the spinein the corrected state. Also shown is locking mechanism 23, used tosecure each pedicle lengthening implant 2 in its extended position.

FIG. 5 a illustrates a three segment portion of a spine with a kyphoticdeformity. The basic anatomic components of the vertebra, includingspinous process 5, transverse process 7, superior articular process 13,inferior articular process 14, pedicle 9 and vertebral body 1 are shown,as well as the neural foramen 27 that allows the nerve root to exit thespinal canal. The posture of the three vertebral segments is seen tocurve anteriorly, as shown by arc 33, thus representing a kyphoticdeformity.

FIG. 5 b illustrates the three segment portion of the spine of FIG. 5 a,demarcating the location of corrective pedicle osteotomies. Lines 35along the base of each pedicle 9 represent the location of therespective pedicle osteotomy, to allow for deformity correction.

FIG. 5 c illustrates the three segment portion of the spine of FIG. 5 afollowing correction of the kyphotic deformity by pedicle lengthening,in accordance with one embodiment of the invention, and stabilization ofthe three segment portion of the spine by securing the pediclelengthening implants 2 with a longitudinal member (rod 17). Note thatthe pedicles 9 have been sectioned at their base and the pediclelengthening implants 2 have been extended to impart an anteriorlydirected force vector 37 to the vertebral bodies 1. This anteriorlydirected force vector 37 pushes the vertebral body 1 forward to reducethe kyphosis seen in FIGS. 5 a and 5 b. This sagittal plane curve may becorrected until a lodotic posture arc 33 has been achieved.Stabilization of the deformity correction is shown by the attachment ofrods 17 to screw head connectors 21 which have been attached to thepedicle lengthening implants 2.

Method of Operation:

Methods for achieving, and operation of implants to achieve, expansionof the spinal canal, with simultaneous stabilization of the spine,involve, first, cutting and lengthening the pedicles of thepathologically involved vertebral segments. Methods and implants forpedicle lengthening are disclosed in U.S. Pat. No. 7,166,107 and/or U.S.application Ser. No. 12/624,946—each incorporated herein by reference.The pedicle lengthening implants 2 can be implanted, and the necessaryexpansion of the spinal canal 15 can be achieved through the threadablemovement of the jack screw 19 of the pedicle lengthening implant 2,until the desired expansion of the spinal canal is achieved. Next, alocking mechanism 23 is threadably applied to each pedicle lengtheningimplant 2 to secure the pedicle lengthening implant 2 in its expandedstate. A screw head connector 21 is attached to each pedicle lengtheningimplant 2. Attachment of the screw head connector 21 to the jack screw19 is achieved using methods well known in the art of spinal surgery.Next, a longitudinal member, such as a rod 17 or plate, is attached tothe screw head connector 21 and secured with a locking nut 25 or asimilar securing/locking mechanism.

Aspects of the present invention can also be used to attach alongitudinal member (rod 17 or plate) to existing pedicle lengtheningimplants 2 (i.e., pedicle lengthening implants inserted by a priorsurgery). In this situation, the screw head connector 21 is attached toa dorsal portion of the prior pedicle lengthening implant 2. A rod 17(or similar longitudinal member) can then be attached to the screw headconnector 21 and secured with a locking nut 25 or a similarsecuring/locking mechanism.

When aspects of the present invention are used to correct a rotationaldeformity, the pedicle lengthening implants 2 should first be insertedinto the pedicles 9 (as detailed and referenced above) of therotationally deformed vertebra. After cutting both the right and leftpedicles 9, the pedicles 9 are lengthened in an asymmetric fashion, sothat the shorter pedicle 9 is lengthened more than the longer pedicle 9.In some cases, the longer pedicle 9 may actually be maintained withoutlengthening, while the shorter pedicle 9 is lengthened to achieve thedesired degree of rotational correction. Once the desired degree ofrotational correction is achieved, the locking mechanism 23 is appliedto the jack screw 19, to keep the pedicle lengthening implant 2 in thedesired expanded position. In cases where the rotation deformity is partof a major spinal curve such as scoliosis, the pedicle lengtheningdevices 2 should then be attached to longitudinal members (rods 17 orplates) to stabilize and correct the spinal curvature. To achievecorrected curvature, a screw head connector 21 is attached to a dorsalportion of each pedicle lengthening implant 2. The screw head connectors21 are then attached to rods 17, or other longitudinal members, and aresecured to the rods 17 with a locking nut 25 or to a similarsecuring/locking mechanism.

When aspects of the present invention are used to correct kyphosis ofthe spine, pedicle lengthening implants 2 are first implanted into thepedicles 9 of a kyphotic segment of the spine. During the pediclelengthening maneuver, the pedicles 9 of the vertebrae at the apex of thedeformity are lengthened the most, with slightly less lengthening doneat the vertebrae adjacent to the apex of the deformity. By lengtheningthe pedicles 9, an anteriorly directed force vector 37 is produced,which moves the vertebral bodies 1 in an anterior direction, resultingin correction of the kyphotic deformity. Once the desired degree ofcorrection is achieved, the locking mechanism 23 is applied to maintainthe pedicle lengthening device 2 in the desired expanded position. Next,screw head connectors 21 are attached to a dorsal portion of the pediclelengthening implants 2 (as mentioned above). The screw head connectors21 can then be attached to rods 17, or to other longitudinal members,and are secured with a locking nut 25 or to a similar securing/lockingmechanism.

What is claimed is:
 1. An implant system for expanding a spinal canaland stabilizing vertebrae, the implant system comprising: a pediclelengthening implant inserted into a first vertebra, the pediclelengthening implant comprising: an outer sleeve having an upper portionand a lower portion; and an inner member communicating with the outersleeve, wherein movement of the inner member in relation to the outersleeve causes the inner member to translate the upper portion away fromthe lower portion, about a vertebral cut, to widen the vertebral cut andto thereby expand the spinal canal; and a longitudinal member attachedto the pedicle lengthening implant, the longitudinal member alsocommunicating with an implant inserted in a second vertebra to fixatethe first vertebra to the second vertebra.
 2. The implant system ofclaim 1, further comprising a locking mechanism, applied to the pediclelengthening implant after operating the pedicle lengthening implant towiden the vertebral cut, the locking mechanism applied dorsal of andabutting the upper portion, to secure the pedicle lengthening implantand the widened vertebral cut.
 3. The implant system of claim 1, furthercomprising a screw head connector attached to a dorsal portion of thepedicle lengthening implant to attach the longitudinal member to thepedicle lengthening implant, wherein the longitudinal member is attachedto the screw head connector.
 4. The implant system of claim 3, whereinthe screw head connector includes a securing mechanism therein to securethe longitudinal member to the screw head connector after inserting thelongitudinal member through an opening in the screw head connector. 5.The implant system of claim 4, wherein the securing mechanism is alocking nut within a dorsal end of the screw head connector.
 6. Theimplant system of claim 1, wherein the longitudinal member communicateswith the second vertebra by attachment to a respective second pediclelengthening implant implanted in the second vertebra.
 7. The implantsystem of claim 6, wherein a spinal deformity is manipulated, throughoperation of the first or the second pedicle lengthening implant,respectively within the first or the second vertebra, to improve arelative relationship between the first and the second vertebra, and thelongitudinal member then fixates the first and the second vertebra intoa multi-level spinal construct.
 8. The implant system of claim 7,wherein attachment of the longitudinal member to the first and thesecond pedicle lengthening implant treats one or more of kyphosis,scoliosis or rotational deformity of a spine.
 9. The implant system ofclaim 1, wherein the inner member threadably engages at least a portionof an inner channel of the outer sleeve.
 10. A method for expanding aspinal canal and stabilizing vertebrae, the method comprising the stepsof: drilling a passage into a first vertebra; performing a cut generallyperpendicularly to the passage through the first vertebra; inserting thepedicle lengthening implant of claim 1, or claim 9, into the passage;operating the pedicle lengthening implant to widen the cut; andattaching a longitudinal member to the pedicle lengthening implant,wherein the longitudinal member also communicates with an implantinserted in a second vertebra to fixate the first vertebra to the secondvertebra.
 11. The method of claim 10, repeated in a second vertebra,wherein operating a second pedicle implant of claim 1, or claim 9,widens a cut in the second vertebra, and attaching the longitudinalmember to the respective pedicle lengthening implants fixates the firstvertebra to the second vertebra, to correct one or more of a rotationaldeformity of a vertebra, a kyphotic deformity of a spinal column, andscoliosis of a spinal column.
 12. The method of claim 10, wherein adeformity is manipulated, through operation of one or both of therespective pedicle lengthening implants, within the first and/or thesecond vertebra, to improve a relative relationship between the firstand the second vertebra, and the longitudinal member then fixates thefirst and the second vertebras into a multi-level construct.
 13. Theimplant system of claim 1, wherein the upper portion and the lowerportion include external threads to engage a vertebra about each side ofthe vertebral cut, the upper portion engaging one side of the vertebralcut and the lower portion engaging another side of the vertebral cut.14. The implant system of claim 13, wherein the inner member threadablyengages an inner channel of the upper portion to translate the upperportion away from the lower portion about the vertebral cut to widen thevertebral cut.
 15. The implant system of claim 14, wherein the innermember, after threadably engaging the inner channel of the upperportion, bears against the lower portion, to translate the upper portionaway from the lower portion about the vertebral cut to widen thevertebral cut.
 16. An implant system for expanding a spinal canal andstabilizing vertebrae, the implant system comprising: a pediclelengthening implant inserted into a first vertebra, the pediclelengthening implant including: an upper portion and a lower portion,each having an inner bore; an inner member extending into the inner boreof, and interacting with, each of the upper and the lower portions, theinner member extending therein generally defining an implantlongitudinal axis; wherein: rotating the inner member about the implantlongitudinal axis translates the upper portion away from the lowerportion, along the implant longitudinal axis, about a vertebral cut, towiden the vertebral cut, thereby expanding the spinal canal; and alongitudinal member attached to the pedicle lengthening implant, thelongitudinal member also communicating with an implant inserted in asecond vertebra to fixate the first vertebra to the second vertebra. 17.The implant system of claim 16, further comprising a locking mechanism,the locking mechanism threadably engaging the pedicle lengtheningimplant, dorsal of and abutting the upper portion, to secure the upperportion relative to the lower portion along the inner member, about thewidened vertebral cut.
 18. The implant system of claim 16, furthercomprising a screw head connector attached to a dorsal portion of thepedicle lengthening implant to attach the longitudinal member to thepedicle lengthening implant, wherein the longitudinal member is attachedto the screw head connector.
 19. The implant system of claim 16, whereinan externally threaded proximal member extends dorsally from the pediclelengthening implant, along the implant longitudinal axis.
 20. Theimplant system of claim 19, further comprising a locking mechanism, thelocking mechanism threaded internally to engage the proximal member, andthreadably translate about the proximal member, along the implantlongitudinal axis, to abut the upper portion, to secure the upperportion relative to the lower portion on the inner member.
 21. Theimplant system of claim 20, further comprising a screw head connectorthreadably receiving the proximal member, the screw head connectorreceiving therethrough the longitudinal member.
 22. The implant systemof claim 21, wherein the screw head connector further comprises alocking nut within a dorsal end thereof to secure the longitudinalmember therein.
 23. The implant system of claim 16, wherein the innermember extends completely through and dorsally from the inner bore ofthe upper portion, and wherein a locking mechanism, engages the dorsallyextending inner member to abut the upper portion, and to secure theupper portion relative to the lower portion on the inner member.